Oxidation of 4, 11-dichloro-6, 13-dihydroquinacridone



unitidstates iflf 9 v a r 3,301,856 OXIDATION OF 4,11-DICHLOR-6,13-DIHYDRO- QUINACRIDONE I James F. Higgins, Livingston, N.J., as'signo'r to E. I. du Pont' de Nemours and Company, Wilmington, Del., a

corporation of Delaware FiledDe'c. 20, 1965, Ser. No. 514,803

2 Claims. (Cl. 260-479) This invention relates to an improved method for the preparation; of 4,11.-dichloroquinacridone and more particularly to an improvement in the method of oxidizing 4,11-dichloro-6,IS-dihydroquinacridone to 4,11-dichloroquinacridone. 1 x

U;S. Patent'2,821,529 discloses the oxidation of 6,13- dihydroquinacridone in a, medium composed of an alkali, an alcoholic solvent and water. No critical proportions of the ingredients are specified in this patent.

Morerecently'it has been shown that certain critical compositions offer specific advantagesin the oxidation of unsubstituted; 6,l3-dihydroquinacridone toquinacridone. US. Patent 2,969,366 discloses that a specific critical area of composition incorporating relatively high amounts of alkaliand fairly'high amounts of alcohol with correspondinglyxlowamounts of water is essential to good phase controland-causes the oxidation to take place essentially iIl'SOlllliOl'l. In like manner, US. Patent 3,007,930 discloses a composition low in alkali and relatively high in water critical to the formation of gamma phase quinacridone if the dihydroquinacridone; being oxidized has previously been converted to the beta phase.

-.Serial No." 336,959, filed January 10, 1964, shows that when a very limited area of composition containing an appreciably higher amount of alkali than .was used in US. Patent 3,007,930, but with a restricted area of alcohol and water composition is used with alpha phase dihydroquinacridone, abetaphase quinacridone of particularly advantageous'properties is obtained.

Laboratory research has'found that the oxidation of 4,1l-dichloroquinacri'done is relatively easy .to accom: plish within a rather wide area of compositionsbut that, when it is done with compositions containing relatively large amounts -.of alkali, theresulting composition is inevitably a sodium salt of 4,1l-dichloroquinacridone which is not readily hydrolyzed to the' free 4,11-dichloroquinacridone. Consequently, it has required a two-step operation, first the oxidation itself and second a specific hydrolysis under acid conditions, to bring about the desired formation of 4,1l-dichloroquinacridone. Therefore, it has been an unsatisfied need to enable the oxidation of 4,1l-dichloro-6,13-dihydroquinacridone to 4,1l-dichloroquinacridone in an economical one-step operation. A medium which contains the least possible amount of alcohol will keep the costs as low as possible.

It is an object of this invention to carry out the oxidation of 4,1l-dichloro-6,l3-dihydroquinacridone in a medium consisting of water, methanol and sodium hydroxide under conditions where a separate hydrolysis step is not necessary and where the least possible amount of alcohol may be used.

It has now been found that in the process of oxidizing 4,1l-dichloro-6,13-dihydroquinacridone to 4,11-dichloroquinacridone with nitrobenzene-meta-sodium sulfonate in a solvent mixture of water, methanol and sodium hydroxide, there is a critical area of composition within which the oxidation is effectively and economically carried out in a simple one-step operation. The effective limits for this operation are found between a water content of 70 to 90%, 21 methanol content of 5 to 24%, and a sodium hydroxide content of 2 to In a preferred embodiment of this invention, 4,11-

fonate as the oxidizing agent.

Patented Jan. 31, 1967 dichloro-6,13-dihydroquinacridone is dispersed in a medium comprisingabout,80% water, about 15% methanol, and about 5% sodium hydroxide to which is then added an appropriate amount of nitrobenzene-meta-sodium sul- The mixture is then heated at the boil under reflux for a significant period of time, after which the resulting red pigment is isolated from the mixture by conventional means.

Theaccompanying'drawing is a ternary diagram for the system water-sodium hydroxide-methanol, and it shows the useful area for this invention.

'For ,a clearer understanding of the invention, the following specific examples are given. These examples are merely intended to be illustrative of the invention and not in limitation thereof. Unless otherwise specified, all parts are by Weight.

EXAMPLE I 20 parts of 4,11-dichloro-6,13-dihydroquinacridone (obtained by condensing o-chloroaniline with a dialkylsuccinylsuccinate, and cyclization of the product by heatingin an inert liquid diluent followed by isolation from the diluent) is dispersed in a solution of 60 parts methanol in 260 parts water to which is then added parts of a 50% aqueous solution' of sodium hydroxide. After stirring for about S'minutes, 20 parts of nitrobenzenemeta-sodium sulfonate is added. The mixture is heated rapidly to the boil and boiled under reflux for about 4 hours. The 4,1l-dichloroquinacridone is isolated in quantitative yield by filtering, washing free of alkali and drying. After suitable particle size reduction, it is a reddish-orange pigment of good intensity and high strength. In the crude form, it is useful as an ingredient in the preparation of a scarlet pigment comprising a solid solution of about 40 parts of 4,1l-dichloroquinacridone and 60 parts quinacridone (see US. Patent 3,160,510). This solid solution is readily obtained during the particle size reduction step by ball milling the two components together with hydrated aluminum sulfate as the milling aid in the presence of a small amount of an organic solvent such as tetrachloroethylene and subsequently extracting the water soluble milling aid.

EXAMPLE II The procedure of Example I is repeated except that the solvent medium consists of 300 parts water and 60 parts methanol to which is added 40 parts of a 50% aqueous solution of sodium hydroxide. The results are identical to those of Example I.

The following table shows the weight percent composi tion of the solvent media in Examples I and II as well as a number of other compositions which give equivalent results:

Table l Methanol NaOH These points are identified on the accompanying drawing by the symbol x and by a number corresponding to the example number given above.

sodium hydroxide as the alkali.

In contrast to the above, the following compositions are not effective for the purpose of this invention as shown:

These points are identified on the accompanying drawing by the symbol 6 and by a letter corresponding to the example letter given above. The drawing further illustrates on a ternary diagram the useful areaof this invention which is outlined by heavy solid lines.

The method by which the 4,11-dichloro-6,l3-dihydroquinacridone is prepared is not critical ,to this invention. The method suggested in Example I is a convenient one but other methods, where available, may be useful. It is known that this product exists in at least two crystal modifications and it is further known that the results of the oxidation may be effected to some degree by the crystal modification to which the oxidation step is applied. However, the important advantage of this invention (to carry out the oxidation in a one-step process and obtain complete oxidation in an economical solvent mixture) is accomplished regardless of the phase of the raw material to which the invention is applied. Furthermore, in the principal use of 4,1l-dichloroquinacridone (the formation of solid solution with quinacridone to give a scarlet pigment) the process of forming the solid solution is independent of the character or crystal phase of the 4,1l-dichloroquinacridone to which the process is applied.

The critical proportions defined in this invention are set forth for methanol as the alcoholic solvent and for Similar results can be obtained, however, with other water soluble alcohols such as ethanol or isopropanol and with other strong alkalies such as potassium hydroxide and even barium hydroxide. However, the critical proportions for these other agents will vary in view of the different equivalent weights of the alkalies and the different molecular weights of the alcohol. Another important factor is the tendency of the higher alcohols to form two-phase mixtures with water in the presence of alkalies. Hence, there is a significant advantage in the use of methanol because of the range of mutual solubility with mixtures of Water and sodium hydroxide.

The preferred oxidizing agent shown in the examples is nitrobenzene-meta-sodium sulfonate. This is preferred primarily because of its .ready availability but other aromatic nitro compounds arev useful includingthe sodium salts of nitrotoluene sulfonic acid, of nitrobenzoic acid, and of nitrophthalic acid, and even nitrobenzene itself. The amount of oxidizing agent is not critical as long as it is in suflicient quantity to provide complete oxidation of the dihydro quinacridone. It is common practice to use substantially the same weight as the dihydroquinacridone being oxidized but this may be reduced to 75% or even as little as 50% of the weight of the.dihydroquinacridone.

, The amountof the liquid reaction medium with respect to the dihydroquinacridone being treated is not especially critical as long as there is sufficientliquid to give a fluid slurry for good agitation. It has been shown in the examples that it is the composition of the liquid reaction medium which is critical to this invention rather than the total amount used in relation to thedihydroquinacridone. There must be at least about5% alcohol and not more than 90% water. The alcohol need not exceed about 24% and the water should not be less than about 70%. 7

When less than 2% sodium hydroxide is used, the oxidation is incomplete.v On the other hand, when the sodium hydroxide exceeds about 10%, the undesirable formation of the sodium salt, which is difiicult to hydrolyze, occurs. These limits are clearly set forth in the area defined by the hexagonal figure on the accompanying drawing.

This invention offers an advantage with respect to the prior art methods of oxidizing 4,ll-dichloro-6,13-dihydroquinacridone in two respects. In the first place, it gives a complete oxidation without the formation of a sodium salt which requires an extra hydrolysis step to convert it back to the free 4,1l-dichloroquinacridone. In the second place, it enables operation with a relatively small amount of the more expensivev alcoholic solvent so that there are inherent economies in the operation;

What is claimed is: 1. In the process of oxidizing 4,11-dichl-oro-6,13-dihydroquinacridone to 4,1l-dichloroquinacridone with nitrobenzene-meta-sodium sulfonate in a solvent mixture of water,- methanol and sodium hydroxide, the iinprovethe sum of these components always being 100%.

2. The improvement of.claim' 1 wherein the composition of said solvent mixture is about water, about 15%- methanol and about 5% sodium hydroxide.

H I No references cited.

ALEX MAZEL, Primary Examiner. DONALDG. DAUS, Assistant Examiner. 

1. IN THE PROCESS OF OXIDIZING 4,11-DICHLORO-6,13-DIHYDROQUINACRIDONE TO 4,11-DICHLOROQUINACRIDONE WITH NITROBENZENE-META-SODIUM SULFONATE IN A SOLVENT MIXTURE OF WATER, METHANOL AND SODIUM HYDROXIDE, THE IMPROVEMENT WHICH COMPRISES LIMITING THE COMPOSITION OF SAID SOLVENT MIXTURE TO A WATER CONTENT OF ABOUT 70% TO ABOUT 90%, A METHANOL CONTENT OF ABOUT 5% TO ABOUT 24%, AND A SODIUM HYDROXIDE CONTENT OF ABOUT 2% TO ABOUT 10%, THE SUM OF THESE COMPONENTS ALWAYS BEING 100%. 